The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
An automatic transmission within a vehicle is a device for automatically changing power that is supplied from a power generation device, such as an engine or the like, to torque and rpms for a smooth driving.
As transmission ratios that can be internally implemented in the automatic transmission become various, power supplied from the power generation device may be more suitably changed depending on the driving state of the vehicle, and the fuel efficiency and power performance of the vehicle may be improved.
In order to implement various transmission ratios, controlling multiple friction elements as well as making good shift quality without shift shocks by precisely controlling the respective friction elements is desired. Also, the friction elements may be operated depending on a fixed combination, and a fail-safe function may be desired to avoid the possibility of malfunction and perform the minimum operation even in the event of failure.
In a conventional art, each of solenoid valves for providing hydraulic pressure to the friction elements is connected to a fail-safe valve, where the occurrence of an interlock situation may be inhibited. However, when a number of friction elements are used for the implementation of a multi-range transmission, the cost of applying fail-safe valves may increase.